This invention relates to a cutter bit and a cutter bit assembly for cutting or winning.
Known cutter bit assemblies have bits having a conical cutter head and a cylindrical shank which is rotatably and replaceably insertable within a cylindrical bore of a cutter bit holder, the shank being secured against axial displacement in the bore by means of an elastic securing ring arranged in a reduced-diameter part of the cutter bit shank.
German Utility Model DT-Gbm No. 1,923,922 describes a cutter bit assembly in which the shank of the cutter bit is secured in the bore of the bit holder by means of an elastic securing ring of synthetic plastics material, rubber or the like which is seated in a groove in the bit shank and which engages in an annular groove in the bore or behind a shoulder provided in the bore. The bit is, therefore, secured by a detent-type connection. In this case, it is necessary to adapt the annular groove or the shoulder in the cylindrical bore very precisely to the position of the securing ring on the bit shank, in order to ensure that when the shank is inserted into the bore the securing ring engages in the groove or behind the shoulder. In the case of deformation or soiling of the bit holder a reliable connection is not always guaranteed. Another disadvantage of this assembly is that the shank (and hence the bit) cannot rotate about its axis, by reason of the frictional engagement with the securing ring, rotatability of the cutter bit being important in order to ensure the most uniform possible wear of the bit and the self-sharpening attendant effect.
German printed publication DT-OS 2330297 and German Pat. No. DT-PS 1940577 describe a cutter bit assembly in which the bit shank is rotatably held in a bearing bush of hardened and abrasion-resistant material, the bush being in turn rotatably mounted in the bore of the holder and secured against axial withdrawal by a circlip or the like. In order to secure the bit shank in the bearing bush, a slotted spring ring of metal is provided which sits in an annular groove in the bit shank and is provided with radial pressed-out portions, dogs or the like which engage in an annular groove in the cylindrical wall of the bore of the bearing bush. Here again, the axial securing of the bit shank is effected by a detent-type connection which requires precise fitting.
U.S. Pat. No. 3,342,531 describes a cutter bit which is detachably secured in the bore of its bit holder by means of spring-loaded locking members.
The aim of the invention is to develop a cutter bit which is rotatable within its holder without the need for cutting a detent groove, for the securing element, in an accurately predetermined position in the cylindrical inner wall of the bore in the holder. Moreover, the cutter bit should be capable of easy and rapid replacement.